1. Field of the Invention
The invention generally relates to actuators used to control the phase relation between the expander and displacer portions of Stirling engines, and more particularly to a hydraulic actuator which takes advantage of variations in torque requirements for the displacer portion of a Stirling engine during each rotation thereof, whereby the phase relation between the expander and displacer is varied through use of minimal external force.
2. Description of the Prior Art
The name Stirling engine frequently is indescriminantly applied to various types of regenerative machines, including both rotary and reciprocating engines, utilizing mechanisms of varying complexity and covering machines capable of operating as prime movers, heat pumps, refrigeration engines and pressure generators. However, for the purpose of the invention as herein disclosed it is to be understood that a Stirling engine is a device particularly designed to operate on a closed regenerative thermal dynamic cycle and is characterized by a cyclic compression and expansion of a working fluid at different temperature levels with flow control for the fluid being established by volumetric changes so that a net conversion of heat to work or work to heat is realized.
While Stirling engines frequently are provided with two pistons connected to a common crankshaft and equipped with a heat exchanger connected between the pistons, it is known that a Stirling engine also can be so constructed as to employ two pistons connected to separate crankshafts. Hence, as herein employed the term expander portion of a Stirling engine refers to that portion of the engine having a crankshaft and within which hot gases are expanded for converting heat energy to work, while the term displacer portion of the engine refers to that portion of the engine having a crankshaft to which a piston is connected for utilizing power transmitted thereto from the expander portion to compress a cool working gas. It is to be understood that the displacer portion of the engine, herein referred to in operation, experiences torque requirements ranging between both positive and negative torque input during each cycle of operation, while the output of the expander portion simultaneously undergoes changes ranging between 0 and positive value. The phase positive and negative torque refers to force input during unidirectional rotation of the crankshafts.
The performance of a Stirling engine having dual crankshafts, or separate crankshafts for the expander and displacer portions, is dependent in large measure upon the phase relation established between the dual crankshafts, much in the same manner that the power of an automobile engine is dependent upon the timing of the ignition system. For example, where the phase angle between the crankshafts is zero there is little or no power output, where the phase angle is approximately positive 90.degree. the power output is maximum in a "forward" rotation; and where the phase angle is approximately negative 90.degree. the power output is a maximum in a "reverse rotation".
It is, of course, known that the phase relation control between dual crankshafts can be achieved through the use of a force transfer gear meshed with a pair of coaxially spaced bevel gears, separately mounted on the crankshafts, and supported by a carrier arm for planetary travel relative to the bevel gears. For example, see U.S. Pat. No. 3,315,465.
During the course of a search conducted on the invention herein described and claimed, the following additional U.S. Pat. Nos. were discovered:
3,482,457 which relates to hydraulically actuated, differential geared Stirling engine phase changers;
3,315,465, 3,416,307, and 3,416,308 which relate to low torque Stirling engine phase changers with differential gears; and
2,465,139, 2,508,315, 3,994,136 and 4,074,530 which relate to other mechanical Stirling engine phase changers.
Of course, phase changes between the expander and displacer portions of a Stirling engine usually require application of substantial torque. The amount of torque normally required is greater than which can conveniently be derived from a simple hand lever. Consequently, because of the large amounts of force required in achieving a phase-change relation between the expander and displacer portions of a Stirling engine, there currently exists a need for a simple device through which an operator may readily adjust the speed/power for such an engine, without requiring that the operator manually apply large amounts of force, regardless of whether the engine is operating or is quiescent.
It is therefore the general purpose of the instant invention to provide phase-angle control means coupled with the crankshafts of a Stirling engine and adapted to be used in establishing variable phase-angle relationships between the crankshafts utilizing variations in torque requirements of the displacer portion of the engine during each rotation of the crankshafts, without sacrificing the utility of the engine or power outputs thereof.